yihua commented on code in PR #13675:
URL: https://github.com/apache/hudi/pull/13675#discussion_r2274768726
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hudi-common/src/main/java/org/apache/hudi/metadata/ColumnStatsIndexPrefixRawKey.java:
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@@ -25,40 +25,64 @@
import java.util.Objects;
/**
- * Represents a raw key for column stats index consisting of column name and
optional partition name.
+ * Represents a raw key prefix for column stats index consisting of column
name and optional partition name.
+ * <p>
+ * This key is used for prefix lookups in the COLUMN_STATS partition to find
all stats
+ * for a specific column across files, or for a column within a specific
partition.
+ * This enables efficient retrieval of column statistics for query planning.
+ * <p>
+ * Raw key format:
+ * - Column-only lookup: base64(column_name)
+ * - Column + partition lookup: base64(column_name) +
base64(partition_identifier)
+ * <p>
+ * Examples:
+ * - To find all stats for column "price" across all partitions and files:
+ * key = base64("price")
+ * Example encoded: "cHJpY2U="
+ * <p>
+ * - To find all stats for column "user_id" in partition "2023/01/15":
+ * key = base64("user_id") + base64("2023/01/15")
+ * Example encoded: "dXNlcl9pZA==" + "MjAyMy8wMS8xNQ=="
+ * <p>
+ * - To find all stats for column "revenue" in non-partitioned table:
+ * key = base64("revenue") + base64("__HIVE_DEFAULT_PARTITION__")
Review Comment:
Non-partitioned table does not use `__HIVE_DEFAULT_PARTITION__`. Removing
this for now.
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